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Goodwill and intangible assets - Narrative (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2020 | Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Goodwill impairment |  |  | $ 0 | $ 0
Relief of goodwill related to the sale of the TPO mortgage delivery channel |  |  |  | $ 100,000
Farmers National | Core deposit intangible |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Intangible assets acquired |  | $ 2,490,000 |  |
Weighted average life of intangible assets acquired |  | 4 years |  |
Franklin Financial Network, Inc. | Core deposit and other intangibles |  |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |  |
Intangible assets acquired | $ 7,670,000 |  |  |
Weighted average life of intangible assets acquired | 4 years |  |  |

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